sulli

Coming back from Devon today, and on the motorway if I floored it (full throttle) in either 4th or 5th at under 3500rpm, when I reached 3500 the car would lurch like it was missing - this sometimes continued higher up the rev range.
Tried a few different scenarios, and basically it wouldn't do this if I accellerated but at say half-throttle, but turbo still winding up. Nor would it do this in 1st, 2nd or 3rd gears.
The car was packed to the roof with camping gear, and also had a full roof box. However, nothing like this happened on the way down, with same amount of stuff.
I had filled up with BP ultimate down there as there were no Shell stations (I exclusively us Optimax), and on the way back, before this happened, I got about 2/3 of a tank of optimax in (hello to the Sti7 owner in Woolaton ).
Not sure whether i had a bad batch of fuel, or something more ominous.
I still have Subaru Proven warranty though - but do have an aftermarket exhaust and decat.
Any ideas?

Oh, and its a MY98 turbo wagon.

Butty

iTrader: (2)

Fuel cut?
3.5k rpm would be about peak boost.
4th & 5th gears see higher peak boost than lower gears and with a higher engine load, due to weight you are tugging along, you've pushed the unmapped ECU further than its been before.

sulli

I'll give another test run tomorrow now car is unloaded and see if I see same condition then.
It's weird how it didn't happen on the way down there though - same weight on car.

911

That will be fuel cut.
It suddenly arrived on my Sti v3 2 years ago, fixed now for good. Get it done before too much damage. My car was boosting at 1.6 bar when it happened!
911

sulli

So what do I get done to cure it?
And will it be covered by warranty?

sulli

Just tried it now with no load on car, and there doesn't seem to be a problem.
It must have been the very heavy weight it was carrying.
Should I get it looked at?

Butty

iTrader: (2)

It won't be a warranty claim as it's probably caused by the decat - which voids it.
May get cured with a different restrictor to the boost solenoid and/or a remap (difficult for the MY97/98 models).

GrantyBoy

check your spark plugs. Same thing happened to my 98 v4 Type R. Turned out the plugs had gone.

sulli

The plugs are Iridium and only a year old - approx. 10,000 miles on them - if they have gone i'd be surprised - but i'll check anyway.
Cheers

911

The only solution that worked for me was to have a Blitz Boost controller fitted at high cost (£800). All the usual cleaning soleniods etc did nothing.
My car had a full decat on about 4 months before the onset of fuel cut(aka over-boost).
911

sulli

Well I ran the tank low yesterday, filled up with Optimax at my local shell, and reset the ECU.
Took it out for a right hammering following this, and today managed to test out the exact same conditions (i.e. 4th and 5th, full throttle from 3000rpm).
As I suspected might happen, the fuel cut is no longer occurring.
My theory is that despite having the full decat, decent Sti exhaust system and Sti filter, the ECu has always coped OK - so it's probably always been boosting just within safe limits.
However, having loaded the car with probably an extra 100-150kg, the ECU had to start learning again with the extra weight. I had no problems on the way to Devon (and maybe didn't go full throttle in 4th and 5th), but on the way back I did, and my ECU had begun to learn that to cope with extra weight more boost/fuel/air etc is required. However it must have just gone over safe boost limit for ECU, and thus initiated the fuel cut.
Resetting ECU has solved this.
Well that's my theory anyway.
So I reckon my mods should be OK without a remap, but I am probably fairly close to limit of ECU with the extra power I have. I don't know if there is a limit of what the standard ECU can cope with, with no fettling at all, but I guess around 260-270Bhp.

911

Good luck!
My 'fuel-cut' was most pronounced in the cool air of an early morning run.
Hope it stays ok for you.
911

Dunki2001

Mine was doing same. had it checked and was reaching 1.1 bar. Garage have reduced it to 0.7bar. Now car is slow. How do you clean the solenoids as somebody mentioned. car is Standard apart from scooby sport box. What is standard boost suppose to be?

Cheers

sulli

Well here's an update on this.
I have just returned from Devon again, except this time the car was even fuller, with additional dog and more gear.
I ensured that I only used Optimax (as I always do at home), and I did not suffer the same problem, despite testing it under exactly the same conditions/load etc.
Therefore, i can only assume that my car is used to optimax, and Optimax is good stuff, and that BP Ultimate, or at least the £25 worth that I got, is crap, and lower octane than Optimax.
Glad I always use Otimax

scooby L

May have been DET(due to the lower octane)resulting in the ecu cutting back the advance to protect the engine.

Do you have a knocklink fitted?

Jay m A

iTrader: (2)

Still seems to me like fuel cut due to overboost.

5th gear fully laden will put the most load on the engine, hence giving the turbo more time to over boost.

Perhaps the on your first trip weather conditions were cooler adding to the over boost problem.

If your last trip was the other day (with high ambient temps) then it may not have been able to make as much boost as per the first trip.

StickyMicky

fuel cut is really violent
slight missing is ovb not, which one was it?

sulli

I think fuel cut - but I could be wrong. Felt like a pretty strong miss - not sure how violent - all a question of perception I suppose.